Single-Stage Batch Distillation: Screencasts

Derives mass balances and Rayleigh equation for single-stage batch distillation.

We suggest you list the important points in this screencast as a way to increase retention.

The changes in temperature and composition of the vapor are plotted versus time for batch distillation of a binary liquid that has an azeotrope.

We suggest you list the important points in this screencast as a way to increase retention.

Important Equations:

Overall differential mass balance: $\frac{dW}{dt}\,=\,-\dot{D}\;\;\;\;I.C.\;\;at\;\;t=0,\;W=W_0$

Balance on more-volatile component (MVC) $\frac{d(Wx_W)}{dt}\,=\,-\dot{D}y_D\;\;\;\;I.C.\;at\;t=0,\,x_w=x_{w0}$

where $$W$$ = total moles in still at any time.
$$W_0$$ = total moles in still at time = 0.
$$\dot{D}$$ = rate of distillate being collected
$$x_w$$ = mole fraction of MVC in still
$$y_D$$ = mole fraction of MVC in vapor phase above still
$$x_{W0}$$ = mole fraction of MVC in still at time = 0.

Rayleigh equation $\int_{x_{w0}}^{x_w}\frac{dx_w}{y_d-x_w}=ln\left(\frac{W}{W_0}\right)$

Overall mass balance $W_0\,=\,W\,+\,D$ where $$D$$ = total distillate collected

Overall mass balance on MVC $x_{D,avg}\,=\,\left(W_0x_{w0}-Wx_w\right)/D$ where $$x_{D,avg}$$ = average mole fraction of distillate collected.